(
If you’re a person, chances are you like music.
Hang on. You’re a person, right? Okay, good, cause I don’t want any weird extradimensional monsters doing Saturday Science. They might use our experiments to eat people or something.
As I was saying, people generally like music. Basically, every culture ever has created music in their own particular style, creating rhythms, melodies, and instruments that are uniquely theirs. It’s almost as if humans are wired for music.
Today, you will be wiring for music (see what I did there?). You’ll be making a homemade speaker out of (mostly) stuff you can find around the house. It looks a bit janky, but it works, and it’s super awesome that it works as well as it does. Along the way, you’ll learn a bit about the science not only of sound, but of rock concerts. And all concerts, really, but I’m partial to rock music myself. Now, this does involve a bit of work with electrical wires, so you’ll want an adult’s help for some of the steps.
Materials
- 3 feet of magnet wire
- Tape
- A small rare-earth magnet (a fridge magnet ain’t gonna cut it for this one, so you’ll have to get a really nice one online)
- 1 sticky note
- Audio cable (you want the kind called “1/8 inch” or “auxiliary cable”)
- 2 alligator clip wires
- Sandpaper
- Scissors
- A table that is not made of metal
- A smartphone
- An adult
- A wire stripper (optional, but very useful if you have one)
Important safety note:
Rare-earth magnets have the potential to be dangerous. They range in strength, but all are stronger than the types of magnets we’re generally used to. Two of them can crash together with astonishing force and mash up anything (like a finger or a toe or whatever) that gets in between. And don’t you even think of eating one!
Process:
- Have an adult help you carefully sand two inches of the colored coating off both ends of the magnet wire. You want it sanded down so the copper is exposed.
- Wind the magnet wire around your finger to form a neat coil. Leave about 3 inches loose on each end. Then slide it off, and secure the coil by wrapping a bit of tape around one section so it doesn’t come uncoiled.
- Tape your rare-earth magnet to the top of your table.
- Stick the sticky note next to the magnet so that it forms a flap over top of it.
- Tape your wire coil to the sticky note (it’s important to tape it well, for reasons I’ll explain momentarily).
- Have an adult help you cut one of the plug ends off the audio cable. Strip the rubber down a few inches to expose the wires inside. You will likely see three wires. You only need to worry about the ones carrying the left and right audio signal information, and they are typically coated in white and red rubber. The third is the ground wire, and it’s either exposed and wound up, or coated in yellow or green rubber.
- Have an adult use the scissors (or the wire stripper; this is where it really helps) to carefully remove a bit of the red/white rubber coating that’s insulating the left and right channel wires. It can be tricky to do without just snipping the wire off entirely, so do your best.
- Clip an alligator wire to one of your audio wires, and clip the other end to one end of your coil. Repeat for the other audio wire and the other end of your coil.
- Plug the remaining intact end of your audio cable into your phone.
- Choose a song and hit play.
- Put your ear down close to the sticky note and listen carefully. What do you hear
- (Optional) if you’re having trouble hearing anything, check your wire connections, make sure the volume is all the way up on the phone, and ensure the coil is taped securely to the sticky note.
Summary
Did you hear some sweet Metallica? Or whatever you were listening to? I don’t know your musical tastes. Hopefully they’re good. It’s pretty quiet, because this is a small homemade speaker, but it’s surprising how clearly the music comes through your sticky note. Believe it or not, this is a legit speaker, and functions the same way as a fancy “real” speaker – whether in some headphones or a giant audio stack at a concert. So how does it work?
The short answer is that a speaker’s job is to take an electrical signal and turn it into sound, and that’s just what your speaker does. But that doesn’t really tell you much. There is a long answer, and it requires a bit of background info to understand: any time electricity flows through a wire, it creates (the technical term is “induces”) a magnetic field in that wire. Moving electricity = magnetism. Got it? Okay. Remember that.
The long answer goes like this:
- Your phone (or Walkman or Discman if you’re retro like that) creates a specific electronic signal that maps to the sound you want it to play.
- That specific pattern of electricity travels down the audio cable via those left and right channel wires (to create stereo sound).
- The electricity travels through the magnet wire. Now, what does moving electricity equal? Ding ding ding ding ding! Magnetism! So now you have an induced magnetic field right above the permanent magnetic field inside your rare-earth magnet.
- These two magnetic fields interact with each other and yank on each other and repel each other, and this causes the sticky note to vibrate. It’s not vibrating much at all, which is why you can’t see it vibrate and why the sound is so quiet.
- The vibrations from the paper transfer to the air, creating a pattern of waves—sound waves.
Speaking technically, the sticky note in your speaker is called a “diaphragm.” A diaphragm (when we’re not talking about the big muscle under your lungs that makes you breathe) is just a thin sheet of something separating one section of an object from another. Vibrate the diaphragm in a speaker and you get sound. If you’ve ever heard a blown out speaker, they make a weird buzzing noise and the sound just doesn’t come out right. That’s because the diaphragm has been torn, which limits the way it can vibrate the air.
Now, think about a microphone, the opposite of a speaker. How do you think it works? If you thought “I bet it has a diaphragm and can convert vibrations into electrical signals” then you were dead on. It works like a speaker, but backward.
And I would be remiss if I didn’t point out that sometimes you want a speaker to make things louder than they normally are. That’s where an amplifier comes in. Anyone with an electric guitar has an amplifier that they plug it into since the guitar by itself is pretty quiet. The amp is part speaker, sure, but that part that gives it its name, the amplifier part, takes the electrical signal coming from the guitar (or the microphone or whatever) and, well, amplifies it. It makes the amplitude of the electricity greater, and when the signal reaches the speaker the sound it turns into is a lot louder than it was when it went in.
So now, ladies and gentlemen, you know a bit about how a rock concert works. And I urge all of you, everywhere, to rock on eternally.
Want more Saturday Science? See all of our at-home activities on the blog or on Pinterest.
